The invention relates to an alternating drive, primarily for bicycles and similar driven vehicles, wherein the vehicle comprises a frame and a driven wheel pivotally connected to the frame, the drive comprises a pair of identically designed drive units with opposite driving directions mounted to respective sides of the frame, each of the drive units comprises respective swinging arms pivoted around a common swinging shaft mounted in the frame to perform alternating swinging motion around the swinging shaft, each swinging arm has a respective driving arm with an edge defining a driving path, the driving units comprise a common driving shaft mounted and pivoted in the frame for circular motion around a driving axis, each driving unit comprises a respective bolt with an axis substantially parallel to the driving axis and connected to and rotating with the common driving shaft along respective circular paths around the driving axis, and a driving wheel connected to and pivoted on the bolt, the driving wheels are pressed to the associated one of the driving paths so that the during the rotation of the driving wheels their surfaces roll in a first and then in a returning second direction along the associated driving path causing thereby the swinging arm to perform an alternating swinging motion, the driving wheels are mechanically connected to each other and in each position they are by 180° angularly offset with respect to each other around the driving shaft, respective flexible ropes are connected to an associated one of the swinging arms, and respective biased rope drums mounted around the shaft of the driven wheel and connected to the driven wheel in a manner that allows transmission of torque to the wheel from the rope drum in a single but mutually different direction of rotation only, wherein said ropes are connected to and wound with respective predetermined number of turns around the associated rope drum so that during the driving operation the number of the turns is changing in a mutually alternating manner.
The term “alternating drive” designates a driving system in which the output element of the driving source which provides the driving power is rotating around a circular path, and this circular motion is converted first into an alternating swinging movement, then the swinging element is used to drive the driven wheel of the vehicle mounted on the frame of the vehicle. A condition of the operation of an alternating drive is to comprise a pair of identical but oppositely positioned driving units, and the driving curves of the driving unit should have a certain overlap so that in any moment at least one oldie units be in driving position.
An alternating drive developed for bicycle applications is described in U.S. Pat. No. 5,833,257 which discloses the properties of such drives in detail. The patent shows several embodiments of which from practical grounds the bar link mechanism shown in FIG. 11 or the cam drive shown in FIG. 16 appears realizable. An obvious advantage of the cam drive lies in that by the appropriate design of the shape of the cam disc the properties of the driving characteristic can be changed within a wide range, however in the embodiment shown the cam disc has a big size and weight and the presence of the cam disc substantially limits the applicability of the swinging element for traction purposes.